The present invention relates to a transmission device, a vehicle wheel equipped with sensors, and a system for transmitting tire condition variables.
It is known, among others, from EP-A-0 806 307 to transmit tire condition variables such as pressure or temperature into the interior of a motor vehicle, for example, to an electronic evaluating or control unit. The arrangement described in EP-A-1 227 944 can also measure driving-dynamics tire quantities or wheel condition quantities such as lateral tire force, longitudinal force (wheel torque) or forces that act in a radial direction on the tire (wheel contact force). In both cases, the data to be transmitted is primarily meant for the automated increase of vehicle safety by electronically controlled brake reactions. In addition, there is the possibility of indicating to the driver any information that is interesting to the driver such as about the measured tire pressure, by way of separate display units. Among others, physical conditions such as inside air pressure, air temperature, temperature of the tire rubber, rubber deformations, noise spectra are considered herein as tire condition variables just as well as characteristics or markings such as tire characteristics, from which age, structural shape, type (summer/winter tire) can be taken.
In a tire pressure control system (TPMS) according to EP-A-0 806 307, each of the four wheels comprises an active transmitter, and partly even an additional transmitter in the spare tire. When a number of receiving devices (antenna, receiver) are provided, disadvantageously and assuming usual transmitting field densities, the signal can be received in every receiving device, in the worst case even in a neighboring vehicle, because transmitters generally use the same carrier frequency range. When developing a transmission device for tire condition variables, there is the problem in the application of high-frequency methods that one objective is to achieve a sufficient radius of the service area, while additionally another objective is to appropriately suppress common channel interferences or avoid other undesirable couplings between several transmitters and receiving devices.